bug#7496: 23.2; copy recursive keymap cause crash

[Eli Zaretskii]

> Date: Sun, 13 Oct 2019 21:38:06 +0000 (UTC)
> From: Drew Adams <drew.adams@oracle.com>
> Cc: ari@mbf.ocn.ne.jp, monnier@iro.umontreal.ca, 7496@debbugs.gnu.org
> 
> > It's easy to reproduce, though: Just eval this form and Emacs will
> > segfault (if it's older than yesterday's):
> > 
> > (let ((map (make-sparse-keymap)))
> >   (define-key map " " map)
> >   (copy-keymap map))
> 
> FWIW, on MS Windows, Emacs 26.3, emacs -Q hangs if I
> do that, after showing this message in the echo area:
> 
>   Re-entering top level after C stack overflow.
> 
> Have to kill the process with the Task Manager.

Thanks for testing.  So the stack overflow protection does kick in.